i tracked every miletank from when i got my century at k until the tranny started failing at k what youre describing sounds totally normal to me i usually got mpg over a tank the gas would ding around miles and take gallons to fill back up i drove miles per day for work so i usually filled up close to when the light came on to keep the fuel pump happy and in case i couldnt found a gas stationdecent price for a while i did however push it to plenty of times and a couple times i never ran out of gas and dont remember ever putting a full gal in but i put in a couple times